Abstract

Six bottlenose dolphin deaths occurred in the Swan Canning Riverpark in 2009. The mortalities occurred in two clusters: three deaths in June 2009 and three deaths in September-October 2009. These deaths occurred in two adult females, one adult male, one sub-adult/adult female, one male calf and one juvenile male. One of the dolphins was in an advanced state of decomposition at the time of recovery and necropsy was not conducted. A full necropsy examination was performed on the remaining five dolphins, although a further individual was in a moderate state of decomposition.

In the four remaining dolphins a variety of lesions were found at necropsy examination. Notable findings in two dolphins included severe skin lesions associated with the presence of ‘tattoo skin disease’ (TSD) due to infection with cetacean poxvirus (Figure 1). Two dolphins had active entanglements, including one with concurrent TSD lesions (Figure 2). A consistent finding in all four dolphins was the presence of significant secondary infections by opportunistic bacterial and/or fungal pathogens. These secondary infections likely reflect: (1) reduced immunological function; (2) epidermal damage by a long-standing entanglement injury, offering a portal of entry for opportunistic pathogens; and (3) epidermal colonisation secondary to TSD lesions with subsequent osmoregulatory disruption of the epidermis caused by exposure to low salinity water. Opportunistic fungal and/or bacterial infections were considered to have led directly to the deaths of two dolphins; however the opportunistic infections observed in the other two were not considered to have directly contributed to their deaths. The infections were likely to have occurred as terminal events secondary to the severe TSD lesions, compounded by low salinity conditions.

This presentation will briefly describe the pathology and epidemiology associated with these mortalities, including the unusually severe presentation of TSD. Background information on the factors known to affect dolphin health will also be discussed, including the potential and controversial role of chemical contaminants.